Project Summary: The long-range goal of the proposed research is to understand the biophysical basis for the function of cyclic nucleotide-gated (CNG) ion channels, and the precise roles that these channels play in physiology and disease. In the coming period we will develop a set of potent and specific chemical probes directed at CNG channels of retinal rods. These probes will be essential tools for unraveling the molecular biophysics and physiological roles of these channels in the retina and many other tissues, and for understanding and treating a number of forms of retinal degeneration. CNG channels are a central component of the visual transduction process, generating the electrical response to light in both rods and cones. CNG channels have a similar purpose in olfactory receptor neurons, where they generate the electrical response to odorants. They are also present in many other cell types, including other cells of the retina, where their functions are largely unclear. The following specific aims will be pursued: 1. To increase the potency, specificity, and membrane permeability of cGMP derivatives directed at CNG channels, by selective modification of the untapped 2'-OH group of the ribose. This surprising discovery should allow us to dramatically increase the toolbox of useful cyclic nucleotides. 2. To develop multivalent cGMP ligands that activate CNG channels with very high affinity and specificity. Dimers of cGMP, linked by polymer chains, are the most potent activators to date of CNG channels. This idea will be extended to cGMP trimers and tetramers that can occupy all four sites on the channel protein. 3. To develop potent and specific blockers of CNG channels, taking advantage of multivalent interactions both inside and outside the pore region. Derivatives of tetracaine will be optimized for pore block and then linked to cGMP with polymer chains to greatly enhance the specificity of block. Relevance: Several types of retinal degeneration involve mutations in proteins called cyclic nucleotide-gated (CNG) ion channels, and a number of other forms are associated with abnormal activity of these channels in photoreceptor cells. In these latter cases it is thought that CNG channels are important in the pathology of the disease. The ability to control CNG channel activity with drugs would be extremely useful for studying disease progression and for treating a subset of these blinding diseases.